The Circulatory System

37.2 The Circulatory system

Components of the Circulatory System • Heart • Blood vessels: arteries, veins, & capillaries • Blood

The Heart is a pump • Pericardium: protective membrane that covers the heart • made of cardiac muscle • the size of your fist, located in the chest cavity between the lungs • Our heart has 4 chambers – Atria: 2 upper chambers • Atria have thinner walls compared to the ventricles • Atria receive blood & pump it to the ventricles

– Ventricles: 2 lower chambers • Ventricles have thick walls compared to the atria • Ventricles pump blood to lungs or the rest of the body

• Blood flows one-way

Blood’s Path through the heart

• O2-poor blood comes from the body in veins to venae cavae into the right atrium (RA) • RA pumps O2-poor blood to the right ventricle (RV) • RV pumps O2-poor blood through pulmonary artery to the lungs (blood drops off CO2 & picks up O2 from alveoli) http://www.classzone.com/books/ml_science_share/vis_sim/hbm05_pg63_heart/ • O2-rich blood returns through pulmonary vein to the left atria (LA) • LA pumps O2-rich blood to left ventricle (LV) • LV pumps O2-rich blood through

Heart is a double pump • Pulmonary circulation: pumps O2-poor blood from the heart to the lungs & returns O2rich blood back to the heart. • Systemic circulation: pumps O2-rich blood from the heart to the

Blood vessels: arteries, veins, capillaries

Arteries • Large, thick-walled, muscular, elastic blood vessels • Carry blood away from the heart • Carry blood that is under great pressure • Usually carry O2-rich blood (except for the pulmonary artery & umbilical artery) • Aorta branches to smaller arteries,

Veins • Capillaries join to make larger vessels called venules, which merge to form veins which merge into superior & inferior vena cava • Blood in veins is not under pressure • Veins have valves to prevent blood from flowing backward • Skeletal muscles around

Capillaries • Capillaries are microscopic blood vessels • Capillary walls are one cell thick • Thin walls enable gases, nutrients, and waste to diffuse into and out of blood to tissue and vice versa

Blood

Red Blood Cells (RBC) • 44% of blood volume is RBCs • RBCs are produced in the red bone marrow • RBCs lose their nuclei before entering blood stream • Stay active for 120 days & then are destroyed by the spleen & liver • Oxygen binds to the ironcontaining hemoglobin in RBC (oxygenated RBCs)

Carbon dioxide in the blood • 70% of CO2 combines in water in the blood to make bicarbonate • 30% travel to lungs either dissolved in plasma or carried by RBCs that have released O2 into the tissue.

White blood Cells (WBC) • 1% of the blood is WBC • Protect your body from diseasecausing organisms

Platelets • Platelets are cell fragments involved in blood clotting (combine with protein fibers called fibrin to form clot) • Platelets are made in the bone marrow • Break down after a week and are removed by the spleen and liver

ABO blood groups

Antigens determine blood type • Blood type is determined by proteins on the surface of RBCs called antigens • Antigens are proteins that trigger an immune response • Antibodies are proteins that react to foreign antigens • An antigen-antibody response results in clumped blood (that is why when a person receives a blood transfusion the proper blood type is given)

Rh factor

Rh Factor • Rh factor, or rhesus factor, is another protein either present (Rh+) or absent (Rh-) on the surface of RBC • Rh factor can cause complications in some pregnancies (Rh- mother carries an Rh+ baby—at birth the mom’s & baby’s blood mix—mom makes anti-Rh+ antibodies which can destroy Rh+ baby in the next pregnancy) • A substance can be given to the mom to prevent production of Rh

What makes the heart pump?

Control of the Heart • Heart rate is set by the pacemaker (a bundle of nerve cells at the top of the right atrium) • Medulla Oblongata in the brain controls the rate of the pacemaker • Electrocardiogram (ECG) can monitor the electrical signals sent by pacemaker to the atria & ventricles to check for abnormal heart rhythms

Blood pressure

Blood Pressure • Pulse is the measure of the pressure exerted on the walls of the arteries • Systolic pressure: high pressure exerted on the walls of an artery when the ventricles contract sending blood through the arteries • Diastolic pressure: low pressure exerted on the walls of an artery when the ventricles relax • Regulating blood pressure is important to make sure it’s not too low (cells will not receive adequate oxygen and nutrients) or too high (walls of arteries will weaken and heart will have to work harder to pump)